This invention relates to an apparatus for protecting a copyright of digital information that is digitally transmitted between an information apparatus for home use and personal computers.
Recently, there have been significant advances in data compression for video and audio signals using digital technologies, so that an accumulation and/or transmission of data can be easily performed. Correspondingly, digitalization in the field of broadcasting has also advanced rapidly. For example, a broadcasting system in which an analog video and/or audio signals are digitally compressed and encoded with high efficiency, using an MPEG (Moving Picture Experts Group) standard, and are transmitted through a satellite and/or cable system has been developed. In general, a digital—broadcasting receiver called a set-top-box has been used for receiving and decoding a digital-broadcast signal.
Furthermore, a digital VCR (Video Cassette Recorder) that can record and reproduce video and audio information, such as a digital TV broadcast signal on magnetic type by employing a compression-encoding method has been developed as an apparatus for home use to record and/or reproduce video and audio signals.
One technology by which a requested program can be selected from received digital signals and in which plural information is multiplexed and transmitted is disclosed in the Japanese published unexamined patent application No. H8-56350. Moreover, a digital VCR that uses rotating magnetic heads is shown, for example, in the Japanese published unexamined patent application No. 5-174496. Furthermore, in the publication “Newly Developed D-VHS Digital Tape Recording System for the Multimedia Era” (IEEE Transactions on Consumer Electronics, Vol. 42, No. 3, August 1996, pp. 617-622), a digital broadcast recording system is disclosed in which a digital broadcast receiver and a digital VCR are connected with a transmission line, such as a digital interface. Japanese published unexamined patent application No. H2-7269 is technology describes a method for protecting a copyright of transmitted information in a case where a digital device is connected to a digital interface. In a case where copying of the digital content of an output from a digital interface is prohibited, the digital content is changed (scrambled) to different codes, and then the different codes are outputted on the digital interface. Therefore, the copyright of the digital contents are somewhat protected, because a digital recording apparatus, which receives the different codes doesn't have the ability to decode the different codes.
When a digital broadcasting signal is recorded and reproduced by using a digital VCR, etc., there is a first disadvantage in that, in transmitting copyrighted information externally between apparatuses through a digital interface, unauthorized interception of and/or tampering with the copyrighted information can occur, even if the copyrighted information is scrambled.
As one example, copyrighted information can be intercepted during transmission between apparatuses, and copy control information included therein can be modified (i.e., tampered with) so as to record the copyrighted information with unauthorized copy control information, e.g. allowing unlimited (i.e., piracy) copying. Accordingly, there is a problem that the pirated copyrighted information can be used again by transmitting the information to a device with a descramble function through another digital interface, even though further use should be prohibited. Accordingly, external transmission and recording of copyrighted information with prohibitive copy control information is disadvantageous in that it is susceptible to copyright piracy.